When I was in fifth grade we had an activity one day where we made t-shirts by using transfer crayons and drawing on a special piece of paper and then ironing it onto our shirts. I was reading Heinlein's The Star Beast at the time and I drew the creature from this edition's cover for my shirt. I decided my creature was to be from the planet Venus, so I added the caption "VENEREAL POWER" to my iron-on drawing of a basically penis-shaped alien monster.

The teacher called me up to the desk and pointed to his dictionary which was open to the definition of the word "venereal" and I learned that day that it meant something other than "from Venus". Meanwhile he was looking down at the floor and shaking slightly and it was only years later that I realized he was trying his best not to burst out laughing. He let me make the t-shirt anyway, and I really wish I still had it, but t-shirts don't last 50 years.

I'm not familiar, why was that term phased out?